Demands have arisen for further improving the performance of electromagnetic motors for reasons such as energy saving and CO2 reduction, and the performance represented by areas such as downsizing, weight reduction, high efficiency, high torque, and high output are rapidly improving daily. When classified in accordance with the direction of a magnetic flux, the electromagnetic motors can be classified into (1) a radial flux motor, (2) an axial flux motor, and (3) a transversal flux motor. Of these motors, the radial flux motor is particularly superior in cost performance, and has conventionally been used in a wide variety of products in the world of industry as a typical mechanical element of a general-purpose actuator. Also, the axial flux motor has the structural feature that can cope with a complicated magnetic path arrangement in three-dimensional directions, but makes the use of widely-used conventional laminated steel difficult. Axial flux motors such as this are particularly applied to the field of medium/large-sized, low-profile, large-diameter motors.
Furthermore, the transversal flux motor has the following feature; a basic unit is formed by a rotor including a permanent magnet, and an armature (which forms a split toroidal core) including an annular coil formed around the rotation axis of the rotor, and a plurality of approximately U-shaped stator cores (to be referred to as U-shaped stator cores hereinafter) are formed so as to cover the annular coil on the circumference around the rotation axis, and two or more basic units are arranged along the rotation axis with a predetermined relative phase angle around the rotation axis. This arrangement can achieve a high torque by multiple poles relatively easily, and can achieve high-efficiency magnetic field generation by the split toroidal core structure. That is, when compared to the radial flux motor and axial flux motor requiring a stator core including a plurality of slots on the circumference around the rotation axis, a coil wound around this slot part, and a dead space for coil assembling and insertion, etc., the transversal flux motor only requires the plurality of U-shaped stator cores to be formed on the circumference around the rotation axis. This generally makes it easy to increase the number of poles. Also, the armature including the toroidal coil and U-shaped stator cores has a structure from which a magnetic flux generated by the coil hardly leaks outside. Since this increases the field generation efficiency of the coil, the transversal flux motor can be expected to be downsized more than the radial flux motor and axial flux motor having the coil end.
When the rotor rotates in the transversal flux motor, a magnetic force which intermittently changes its direction acts on the U-shaped stator cores in the rotation direction. This magnetic force vibrates the U-shaped stator cores. This vibration not only decreases the motor's strength, but also generates noise. Furthermore, as the torque increases, a cogging torque which causes torque variations generally increases as well, and this presumably further increases the generation of vibrations. Therefore, demands have arisen for reducing the generation of vibrations in the transversal flux motor.